

A305999


Number of unlabeled spanning intersecting setsystems on n vertices with no singletons.


7




OFFSET

0,4


COMMENTS

An intersecting setsystem S is a finite set of finite nonempty sets (edges), any two of which have a nonempty intersection. S is spanning if every vertex is contained in some edge. A singleton is an edge containing only one vertex.


LINKS

Table of n, a(n) for n=0..5.


FORMULA

a(n) = A306001(n)  A306001(n1) for n > 0.  Andrew Howroyd, Aug 12 2019


EXAMPLE

Nonisomorphic representative of the a(3) = 6 setsystems:
{{1,2,3}}
{{1,3},{2,3}}
{{2,3},{1,2,3}}
{{1,2},{1,3},{2,3}}
{{1,3},{2,3},{1,2,3}}
{{1,2},{1,3},{2,3},{1,2,3}}


CROSSREFS

Cf. A001206, A051185, A048143, A261006, A058891, A261005, A304998, A305854A305857, A305935, A306000, A306001, A306008.
Sequence in context: A132613 A009763 A340886 * A274464 A028979 A082629
Adjacent sequences: A305996 A305997 A305998 * A306000 A306001 A306002


KEYWORD

nonn,more


AUTHOR

Gus Wiseman, Jun 16 2018


EXTENSIONS

a(5) from Andrew Howroyd, Aug 12 2019


STATUS

approved



